Why do you think that? I read a lot of about grid storage, and I can't come to the same conclusion as you on this one. It's very common to talk about GW in isolation of GWh for storage systems in the press, and for GW to be talked about before GWh.

And if you're used to thinking about utilities, it makes a lot of sense, you think about power capacity, and then the duration afterwards. GW is a more direct way to approach that. If you want to get duration from GWh and GW, you have to do a mental division, which is slower than multiplication.